I used a long narrow tank from a maybe late 80s chevy pickup. Mounted it on the passenger side frame rail just behind the battery. difficult part is fabing up the filler. I'd just take your measurements and head to pick n pull.
I've since gone back to the stock tank under the seat, but you can make other tanks work.


It's easier to get forgiveness than permission!
1946 1/2-Ton Chevy
1953 Chevy 3/4-ton Factory Stakebed